This invention relates generally to phase change memories.
Phase change memory devices use phase change materials, i.e., materials that may be electrically switched between a generally amorphous and a generally crystalline state, as an electronic memory. One type of memory element utilizes a phase change material that may be, in one application, electrically switched between generally amorphous and generally crystalline local orders or between different detectable states of local order across the entire spectrum between completely amorphous and completely crystalline states.
Typical materials suitable for such an application include various chalcogenide elements. The state of the phase change materials is also non-volatile. When the memory is set in either a crystalline, semi-crystalline, amorphous, or semi-amorphous state representing a resistance value, that value is retained until reprogrammed, even if power is removed. This is because the programmed value represents a phase or physical state of the material (e.g., crystalline or amorphous).
When a potential is applied across the phase change memory, conduction may occur. In many cases in phase change memories, the exact location where the conductive breakdown occurs through the phase change memory is subject to considerable variability. As a result, since bits may breakdown at different locations, any given bit may exhibit programming or reading characteristics that are different from other bits in the memory. This means that the programming and/or reading margin must be higher in order to accommodate various characteristics of a whole range of different bits.
Thus, there is a need for better ways to form phase change memories.